With word the Obama administration is dropping its plan to try 9/11 suspects in lower Manhattan, experts say many of the potential alternatives have pitfalls, too.

Military bases appear to offer the best alternative, but millions of dollars in construction would be needed to ready such sites, said security and legal experts.

State and federal prisons have also been mentioned as has the federal courthouse in Alexandria, Va., which already hosted a major terrorism trial.

Still, experts said, many existing facilities had shortcomings for playing host to such a trial.

Further complicating the picture is the possibility a trial on a military compound, bristling with soldiers and weapons, could raise further legal challenges in the event of a conviction.

"If they choose something that causes fear and intimidation, it creates an argument that jurors could not act fairly," said Gerald Lefcourt, a prominent Manhattan criminal defense lawyer.

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A number of military installations within a 60-mile radius from Manhattan have been touted as possible trial venues. Robert Strang, a former Drug Enforcement Administration official who does terrorism-related security consulting, said bases present the best alternatives.

"All of the large bases in our country are equipped to handle military trials . . . They have the security, the courtrooms, the transportation, their own [helicopter] landing pads," said Strang, principal of Investigative Management Group.

However, military officials told Newsday on Friday three of the sites mentioned as possibilities - West Point Military Academy, Stewart Air National Guard Base and McGuire Air Force Base - either lack substantial courtroom facilities, jails or both.

New construction would be required, according to law enforcement experts.

While federal prisons have also been mentioned, one federal judge who didn't want to be named indicated using a jail with restricted access would destroy the notion of a public trial embodied in U.S. law.

Smaller military bases such as Fort Hamilton in Brooklyn, Fort Totten in Queens and Fort Wadsworth on Staten Island have possibilities but they too would require substantial construction, particularly for jails, said the jurist.

"You would have to [build] a fort," the judge quipped, "it is just not doable."

In one way, the Manhattan federal courthouse provides best security because it is connected to the Metropolitan Correction Facility by a tunnel, said a high ranked city police official.

The federal courthouse in Alexandria, Va., site of the trial of accused Sept. 11 conspirator Zacarias Moussaoui, has also been mentioned as a possible trial site.The courthouse area is quiet during the day, unlike congested downtown Manhattan.